1. Field of the Invention
The present invention relates to an apparatus for detecting a speed of a rotating body.
2. Description of the Prior Art
Conventionally, for detecting a speed of a rotating body, a rotation distance of the rotating body is first derived based on a given standard value of rotation detecting sections of a rotary element forming a portion of the rotating body and a portion of a speed sensor and the number of input times of pulse signals derived from an output of the speed sensor. The speed of the rotating body is then derived based on this derived rotation distance and periods of the input pulse signals. However, the signal period is subject an aberration caused by a nonstandard factor or element, such as, deformation of the rotation detecting sections due to a processing failure or due to corrosion, or a rotational speed variation of the rotating body due to deformation thereof.
In consideration of the foregoing, Japanese First (unexamined) Patent Publication No. 63-172966 discloses the following vehicle wheel speed detecting apparatus:
In the speed detecting apparatus of this publication, a rotation sensor includes a sensor rotor having the given number of teeth as rotation detecting sections and arranged to co-rotate with a vehicle wheel, and sequentially produces pulse signals corresponding to the teeth of the sensor rotor. During the brake being released, the newest signal period is compared with the last and before-last signal periods so as to derive a correction coefficient for correcting the newest signal period. Accordingly, the correction coefficients are derived in sequence corresponding to the teeth of the sensor rotor, respectively. On the other hand, during the brake being applied, the newest signal period is corrected based on the correction coefficient which was derived for the corresponding tooth of the sensor rotor immediately before the start of applying the brake.
However, the foregoing speed detecting apparatus has the following problem:
Specifically, when, for example, vibration indicative pulse signals which vary at random are inputted, since the foregoing correction coefficients also vary at random, a detection error of the signal period caused by the above-noted nonstandard factor can not be corrected based on such a correction coefficient whether the brake is applied or released.